A removable inferior vena cava filter will be developed to prevent pulmonary embolism in patients who are temporarily at risk to develop this life-threatening complication. The specific design avoids long-term adverse effects of permanent filters, especially cavel occlusion. It overcomes limitations of other temporary filters which, in presence of trapped clot, either must be implanted permanently or be removed at risk of precipitating the pulmonary embolism they were intended to prevent. Up to 1 million patients per year in the United States may be candidates for such a device. The objective of this research is to refine the design of a prototype system towards optimal efficacy and safety. Trapping efficiency and retrievability will be tested in a physiologic in vitro simulation using standardized clot preparations and human pulmonary clot. Trapping efficiency, retrievability, migration, and endothelial ingrowth will be tested in an acute and chronic sheep model with device dwell times up to four weeks. On completion the applicant will have demonstrated feasibility of a temporary caval filter system that catches clot and permits clot removal. The project will provide a refined and well-characterized system with known efficacy as basis for future clinical evaluation and commercialization. PROPOSED COMMERCIAL APPLICATION: Risk factors for pulmonary thromboembolism include immobilization, orthopedic or abdominal surgery, spinal cord injury, multiple trauma, cardiac disease and neoplasm. the removable filter is to benefit patients with temporary risk of pulmonary embolisms. The largest target group is patients with major lower extremity orthopedic surgery. In 1994, in non-Federal short-stay hospitals, 474,000 patients underwent joint replacement of the lower extremities and 89,000 underwent other repair of lower extremities; in addition 27,000 patients with complications in pregnancy and puerperium would qualify. considering that patients with multiple trauma and those with abdominal surgeries are at higher risk of thromboembolism, the total pool of target patients far exceeds 600,000 per year. These are all patients who are at risk of developing deep venous thrombosis and subsequent pulmonary embolism. Additional target patients are those who already have known deep venous thrombosis in the hospital, an estimated 500,000 annually. Even if only 1/10 of these 1.1 million patients would be referred for placement of the temporary filter, an annual need of more than 110,000 filters would result. Costs of permanent filters range between $600-$1400. An efficient and practical removable filter system could represent an annual market opportunity of 60- 140 million dollars in the United States alone.